Inductive device



' Oct. 4, 1932,

A. J. CHRISTOPHER INDUCTIVE DEVICE Filed March 16. 1932 M- 78.57,,Gn .uzmuzrz on 71.57 3.07 IZ7Z 2 m 701, Get ZSZ, F4 22.52};

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600 |o.doo FREQUENCY IN CYCLES PEI? SECOND [0 OOO l/VVE/VTUR A J. CHRISTOPHER 5y ATTORNEY Patented Oct. 4, 1932 UNITED STATES PATENT OFFICE ARTHUR J. CHRISTOPHER, OF TEANECK, NEW JERSEY, ASSIGNOB '10 BELL TELEPHONE LABORATORIES, INCORPORATED, 015' NEW YORK, N. Y., A CORPORATION OF NEW YORK mnucrrvn nnv rcn This invention relates electromagnetic devices and more particularly to transformers and repeating coils employed in telephone systems. An object of this invention is to increase the frequency range over which an inductive device can effectively function.

A more particular object is to enable a transformer or repeating coil to pass both voice and carrier frequencies covering a wide range of frequencies, such as 100 to 50,000 cycles or higher, with high efliciency.

Another more particular object is to reduce the modulation effect in transformers and repeating coils to prevent undesirable crosstalllsz between adjacent communication channe In certain communication systems both materials having characteristics which ren-" der it capable of transmitting efiiciently both carrier and voice frequencies. One of these materials has a low modulation coefficient and alow permeability at low frequencies, while the other exhibits a higher modulation coefficient and a higher permeability at low frequencies than the first material. Certain alloys of nickel-cobalt-iron when heat treated possess properties required of the first material, while other alloys of nickel-chromiumiron have the characteristicsof the second. A nickel-cobalt-iron alloy comprising approxi mately 69% to 70% nickel, 7% to 8% cobalt and the remainder chiefly iron when properly heat treated has an extremely low modulation coefiicient although its initial permeability at 100 cycles is approximately 7 80. A. heat treated nickel-chromium-iron alloy comprising about 77.5% to 79.5% nickel, 3.6% to 4% chromium and the remainder chiefly iron, on the other hand, has a higher modulation coefiicient. The initial permeability at 100 cycles of laminations of this alloy, however, is above 5,600. When laminations of these two alloys are arranged in parallel in the core of a repeating coil, the coil is capable of transmitting both voice and carrier frequencies in a range of 100 to 50,000 cycles without undesirable modulation effects. As a result one coil instead of two is necessary in communication systems employing both frequencies. In addition the balanced line filters may be eliminated and the more economical unbalanced filters substituted on the oflice side of the transformer. Other alloys of nickel-cobalt-iron and nickel-chromium-iron, the quantity of the constituents of which substantially vary from those stated, may be employed with like results.

An embodiment of the pre sent invention is illustrated in the accompanying drawing in which:

Fig. l represents, in a diagrammatic manner, a repeating coil having primary and secondary windings, the core of the coil consisting of layers or laminations arranged in parallel of nickel-cobalt-iron alloys and nickelchromium-iron alloys.

Fig. 2 is a graph indicating the effective alternating current permeability at various frequencies of the core shown in Fig. 1 together the laminations of each alloymay be variedv with the same characteristic of its'compofrom those employed in the above described core depending upon the frequency range and the modulation coeflicient desired.

The laminations of the nickel-cobalt-iron alloy are heat treated by subjecting them to a temperature of 1000 C. (i 20 C.) for a period of at least one hour in a container which insures their freedom from oxidation and contamination. They are then permitted to cool at a rate not in excess 'of 5 C. per minute.

The heat treatment of the laminations of nickel-chromium-iron alloy consists in placingthem in a non-porous annealing box sealed to efficiently protect them from oxidation or contamination at any time. They are maintained at a temperature between 1050 C. to 1100 C. for a period of at least one hour. The rate of cooling is unimportant except between 525 C. and 325 C. Within this range the rate at no instance exceeds 1 Crper minute. 4

In Fig. 2, curve A represents on a double logarithmic scale the permeability character" 7 inches; and thickness 1% inches. The windings comprise twisted pair conductors of 280 turns. As shown in curve A, at 5,000 cycles,

the permeability of the nickel-cobalt-iron alloy is approximately 590. The permeability of the core of Fig.1 is about 510 as indicated in curve B, although that of the nickel-chromium-iron alloy as shown in curve C at 5,000 cycles is 180.

- Since the total effective permeability of the core of the two alloys over the carrier frequencyrange of 5,000 to 100,000 cycles is substantially controlled by the nickel-cobaltiron alloy, the laminations of this alloy are responsible for the passage of the major portion of the effective flux. In addition to the modulation coefiicients of, these two alloys, the effective modulation is dependent upon the proportional flux conducted by the two materials at any given frequency. While the effective modulation of the composite core is somewhat greater at carrier frequencies than a core consisting entirely of laminations of the nickel-cobalt-iron alloy, it is appreciably less than that of a core composed entirely of nickel-chromium-iron or nickel-iron alloy.

For example, it has been estimated that at a fundamental frequency of 6,000 cycles, the

third harmonic current resulting from the coil containing the core of nickel-chromiumiron alloy is approximately 1/60,000 of the fundamental current; that of a core of nickelcobalt-iron alloy approximately 1/1,000,000 of the fundamental; and that of the above described composite core approximately 1/400,000 of the fundamental.

The initial permeability of the composite core at 100 cycles is 1760 (curve B) while the nickel-cobalt-iron alloy has an initial permeability of less than 800 (curve A). As explained previously, while the addition of the chromium -nickel-iron alloy increases somewhat the efl'ective modulation at carrier frequencies, by more than doubling the initial permeability of the core at 100 cycles, an appreciable improvement in transmission efficiency at'this frequency results. I Consequent ly, the use of the composite core markedly increases the service frequency range of repeating coils without any appreciable sacrifice in carrier frequency transmission.

The invention is not restricted in its application to repeating coils, but may be applied usefully to other transformers and other electromagnetic devices in which it is desired to increase the frequency range for which these devices are highly and uniformly effective.

What is claimed is:

1. An inductive device capable of passing both voice and carrier frequency currents covering a frequency range of 100 to 50,000 cycles, with high efiiciency, comprising a core with windings thereon, said core comprising a plurality of materials differing in their electric and magnetic characterist cs, one of said'materials having a low modulation coeflicient at carrier frequencies and relatively low permeability characteristics at low fre quencies, and another of said materials having a higher modulation coefiicient at carrier frequencies and a higher permeability at low frequencies than the said first stated material.

2. ,An inductive device in accordance with claim 1, in which the material having a low modulation coefficient at carrier frequencies and relatively low permeability at low frequencies is an alloy comprising the elements, nickel, cobalt and iron.

3. An inductive device in accordance with claim 1, in which the material having a higher modulation coefiicient at carrier frequencies and a higher permeability. at low frequencies than the said first stated material is an alloy comprising the elements, nickel, chromium and iron.

4. An inductive device in accordance with claim 1, in which the material having a higher modulation coeflicient at carrier frequencies and a higher permeability at low frequencies than the said first stated material is an alloy comprising the elements, nickel, molybdenum and iron.

5. An in'duc'tive device capable of functioning efficiently in a frequency range of 100 to 50,000 cycles comprising a. core windings thereon, said core comprising laminations of a nickel-cobalt-iron alloy having a low modulation coeflicient at carrier frequencies and low permeability at low frequencies arranged in parallel with other laminations of a nickel-chromium-iron alloy hav- ,ing a higher modulation coeflicient at carrier frequencies and a higher permeability at low frequencies than the iron-nickel-cobalt alloy. 6. An inductive device in accordance with claim 5, in which the nickel-cobalt-iron al- 10y comprises 69% to 70% nickel 7% to 8% cobalt and the remainder chiefly iron.

7. An inductive device in accordance with claim 5, in which the nickel-chromium-iron alloy comprises 77.5% to 79.5% nickel, 3.6%

, to 4% chromium and the remainder chiefly iron.

8. An inductive device comprising a core w1th wlndlngs thereon, said core comprislng laminations of an alloy having a low modulation coeflicient at carrier frequencies, a low permeability at low frequencies, and a composition comprising 69% to 70% nickel, 7% to 8% cobalt andthe remainder chiefly iron arranged in parallel with other laminations of an alloy having a higher modulation coeflicient at carrier frequencies, a

higher permeability at low frequencies than .the said first stated alloy, and a composition comprising 77.5% to 79.5% nickel, 3.6% to 4% chromium and the remainder chiefly iron.

9. A repeating coil comprising a core with windings thereon, said core comprising laminations of nickel-cobalt-iron alloy comprising 69% to 71% nickel, 7% to 8% cobalt arid the remainder chiefly iron, arranged in parallelwith laminations of a nickel-chromiumiron alloy comprising 77.5% to 79.5% nickel, 3.6% to 4% chromium and the remainder chiefly iron.

In witness whereof, I hereunto subscribe my name this 14th day of March, 1932.

.ARTHUR J. CHRISTOPHER. 

